Search Results (42)

Nitrogen oxides (NO_x) emitted mainly from vehicle exhaust significantly contribute to urban air pollution, leading to photochemical smog and secondary particulate matter. Photocatalytic technology has emerged as a promising solution for continuous NO_x decomposition under ultraviolet (UV) irradiation. This study developed an eco-friendly permeable concrete incorporating activated loess and zeolite to improve roadside air quality. The high porosity and adsorption capability of the concrete provided a suitable substrate for a TiO₂-based photocatalytic coating. A single-component coating system was optimized by introducing colloidal silica to enhance TiO₂ particle dispersibility and adding a binder to secure durable adhesion on the concrete surface. The produced permeable concrete met sidewalk quality standards specified in SPS-F-KSPIC-001-2006. Photocatalytic NO_x removal performance evaluated by ISO 22197-1 showed a maximum removal efficiency of 77.5%. Even after 300 h of accelerated weathering, the activity loss remained within 13.8%, retaining approximately 80% of the initial performance. Additionally, outdoor mock-up testing under natural light confirmed NO_x concentration removal and formation of nitrate by-products, demonstrating practical applicability in real environments. Overall, the integration of permeable concrete and a durable, single-component TiO₂ photocatalytic coating provides a promising approach to simultaneously enhance pavement sustainability and reduce urban NO_x pollution. Full article

Nitrogen oxides (NO_x) are major atmospheric pollutants, and their escalating emissions, driven by rapid economic development and urbanization, pose a severe threat to both the ecological environment and human health. Conventional denitrification technologies are often hampered by high costs, significant energy consumption, and stringent operational conditions, making them increasingly inadequate in the face of tightening environmental regulations. In this context, photocatalytic technology, particularly systems based on graphitic carbon nitride (g-C₃N₄), has garnered significant research interest for NO_x removal due to its visible-light responsiveness, high stability, and environmental benignity. To advance the performance of g-C₃N₄, numerous modification strategies have been explored, including morphology control, elemental doping, defect engineering, and heterostructure construction. These approaches effectively broaden the light absorption range, enhance the separation efficiency of photogenerated electron-hole pairs, and improve the adsorption and conversion capacities for NO_x. Notably, constructing heterojunctions between g-C₃N₄ and other materials (e.g., metal oxides, noble metals, metal–organic frameworks (MOFs)) has proven highly effective in boosting catalytic activity and stability. Furthermore, the underlying photocatalytic mechanisms, encompassing the generation and migration pathways of charge carriers, the redox reaction pathways of NO_x, and the influence of external factors like light intensity and reaction temperature, have been extensively investigated. From an application perspective, g-C₃N₄-based photocatalysis demonstrates considerable potential in flue gas denitrification, vehicle exhaust purification, and air purification. Despite these advancements, several challenges remain, such as limited solar energy utilization, rapid charge carrier recombination, and insufficient long-term stability, which hinder large-scale implementation. Future research should focus on further optimizing the material structure, developing greener synthesis routes, enhancing catalyst stability and poison resistance, and advancing cost-effective engineering applications to facilitate the practical deployment of g-C₃N₄-based photocatalytic technology in air pollution control. Full article

This study investigates the relationship between surface properties and microstructural characteristics of photocatalytic composites and their impact on air purification efficiency. High-resolution energy-dispersive X-ray spectroscopy (EDS) mapping and mercury intrusion porosimetry (MIP) were employed to analyze photocatalyst distribution and pore structure quantitatively. The findings demonstrated a strong correlation between TiO₂ coverage on the photoactive surface and NO removal rates and between pore structure characteristics and NO₂ generation rates. Two predictive models were developed to link NOx removal rates with photocatalytic cementitious mortars’ surface and structural properties. A stepwise regression approach produced a second-degree polynomial model with an adjusted R² of 0.98 and a Mean Absolute Percentage Error (MAPE) of 8.34%, indicating high predictive accuracy. The results underscore the critical role of uniform photocatalyst distribution and optimized pore structure in enhancing NOx removal efficiency while promoting the generation of desirable products (NO₃⁻) and minimizing the formation of undesirable byproducts (NO₂). Full article

Air pollution, a major health concern, necessitates innovative solutions such as TiO₂-based photocatalytic building materials to combat its harmful effects. This study focuses on developing high-performance TiO₂ photocatalysts for NO_x removal in building applications, aiming to overcome the limitations of commercial TiO₂. These photocatalysts were synthesized via a hydrothermal method, with parameters such as synthesis time and post-treatment investigated to optimize their properties. Hydrothermal synthesis yielded TiO₂ nanoparticles with reduced aggregation and a high proportion of elongated particles with exposed {010} facets. This resulted in significantly enhanced photocatalytic activity compared to commercial P25 in methylene blue degradation and NO_x depollution. Subsequently, the optimized hydrothermal TiO₂ was successfully integrated into a silica sol–gel coating for application on building materials. The coated concrete demonstrated significantly higher NO_x removal efficiency and lower NO₂ release, achieving a 1.7-fold improvement in overall NO_x removal and significantly higher depolluting effectiveness compared to its P25 counterpart. These findings highlight the potential of hydrothermally synthesized TiO₂ with controlled morphology for the development of high-performance, environmentally friendly building materials with enhanced air purification capabilities. Full article

This study investigated the influence of the composition of photocatalytic dispersions made with second-generation nano-TiO₂ on the air purification performance of photocatalytic cementitious composites. Nine mortar series were prepared, incorporating photocatalytic dispersions of variable content of nano-TiO₂, dispersing agent (superplasticizer), and hydrophobic admixture. The total mass content of nano-TiO₂ in investigated mortars was kept at the same level. For investigated composites, photocatalytic removal of NOx was evaluated under simulated laboratory conditions mimicking polish autumn/winter irradiation conditions. The results indicate that within the tested range of variability, the dispersion composition significantly influenced the granulation of the dispersed nano-TiO₂ particles, which in turn affected the air purification performance of the composites. A predictive model was developed to account for environmental factors potentially influencing photocatalytic performance in urban environments. The model estimated that, depending on environmental conditions and photocatalytic dispersion composition, the composite’s photocatalytic layer could remove up to 1.067 g/m² of NO₂ per year in favorable environmental conditions. Photocatalytic cementitious composites can act as environmentally beneficial composites, contributing to carbon-negative construction practices and improving urban air quality. This highlights the dual benefits of offsetting embedded carbon emissions and enhancing air purification efficiency in sustainable urban infrastructure. Full article

The removal of low-concentration NOx contamination in the urban atmosphere has been regarded as an urgent issue to be solved in the context of urbanization. In the past few decades, TiO₂ photocatalysis has been intensively investigated as an economical, efficient, and environmentally friendly means for the abatement of low-concentration NOx. Up to now, however, there have been few reviews focusing on TiO₂-based photocatalysts for photocatalytic NO removal. In this review article, we will summarize the latest advances in the photocatalytic removal of NOx contamination with TiO₂-based photocatalysts, which have been endowed with the reputation of being star catalysts for atmospheric environment remediation. We will begin with a survey of the mechanistic investigations of photocatalytic NOx removal, focusing on the in situ Fourier Transform Infrared Spectroscopy (in situ FTIR) and Electron Paramagnetic Resonance (EPR) studies and the theoretical calculation of reaction pathways with Density Functional Theory. We will then introduce the test methods and the ISO standards for photocatalytic NOx removal and discuss the effect of reaction parameters (catalyst mass, irradiation conditions, temperature, and humidity). Meanwhile, we also elaborate the latest modification methods to enhance photocatalytic efficiency and summarize the progress in recent years in modified TiO₂-based photocatalysts applied in NOx abatement. Lastly, we will put forward some feasible suggestions. In the end, this review may provide some inspiration in designing more effective TiO₂-based photocatalysts for removing NOx contamination from the ambient atmosphere. Full article

This study explores the development and performance of photocatalytic cementitious composites modified with nano-TiO₂ to address urban air quality and sustainability challenges. Nine mortar series were prepared, incorporating binders with varying carbon footprints and mass contents across different series. The interplay between the fundamental (abrasion resistance) and functional (air purification efficiency) properties of the composites’ surfaces and interfaces was investigated. The photocatalytic removal of airborne pollutants, specifically nitrogen oxides (NOx) and ozone (O₃), was evaluated under simulated environmental conditions. The variations in binder composition influenced the composites’ overall initial carbon footprint and air purification efficiency. The assessment revealed a possible net decrease in carbon emissions over the life cycle of the composite due to the removal of ozone (greenhouse gas) and its precursor—NOx, highlighting the potential of photocatalytic cementitious composites for dual environmental benefits in an urban environment, emphasizing the critical role of surface and interface engineering in achieving carbon-negative composites. Full article

This research investigated the properties of photocatalytic cementitious composites, including their air-purification efficiency. A method of characterizing the removal of airborne pollutants (nitrogen oxides), simulating the actual NO_x concentration and irradiation conditions in Warsaw, Poland, in the autumn/winter season was established. The study analyzed the impact of changes in the composition of cement mortars—partial substitution of the binder with mineral fillers—on the properties of the external photoactive surface of the composite. The designed experimental plan included both quantitative and qualitative variables (type and amount of fillers used). It was found that the photocatalytic performance of the composite was correlated with its pore total content and pore size distribution—the higher the content of mineral fillers, the lower the porosity and the less effective its photocatalytic properties. The selectivity of the photocatalytic NO_x reactions also deteriorated as the content of the mineral fillers increased. The study confirmed the validity of increasing the binder content in cementitious composites to enhance their photocatalytic performance. Full article

This study investigated how the surface characteristics of photocatalytic cementitious composites influenced the effectiveness of air purification from nitrogen oxides (NO_x), with a particular focus on the impact of coarse aggregate exposure on the photoactive surface. Air purification efficiency tests were conducted using a custom-developed procedure that simulated NO_x concentrations and UV irradiance typical of autumn and winter conditions in Warsaw, Poland. The findings revealed that the extent of exposed coarse aggregate on the photoactive surface significantly affected photocatalytic efficiency, reducing the overall NO removal rate by up to 50% compared to the reference value. The use of hydration retarders modified the surface characteristics of the photocatalytic cement matrix, enhancing its photoactive potential. The observed decline in photocatalytic efficiency in composites with exposed coarse aggregate was attributed to the coarse aggregate’s limited ability to retain nanometric photocatalyst particles, which reduced the overall TiO₂ content in the composite’s near-surface layer. Nevertheless, cementitious composites incorporating a first-generation photocatalyst exhibited substantial photocatalytic activity, achieving NO removal rates of up to 340 µg/m²·h for non-exposed variants and up to 175 µg/m²·h for variants with exposed aggregate. These results demonstrated their functionality even under low-intensity UV-A irradiation (1 W/m²), making them suitable for environments with limited sunlight exposure. Full article

VOCs can be used instead of ammonia as a reducing agent to remove NO, achieving the effect of removing VOCs and NO simultaneously. Due to the high energy consumption and low photocatalytic efficiency required for conventional thermocatalytic purification, photothermal coupled catalytic purification can integrate the advantages of photocatalysis and thermocatalysis in order to achieve the effect of pollutants being treated efficiently with a low energy consumption. In this study, samples loaded with Co and Mn catalysts were prepared using the hydrothermal method on Fe-MOF with various morphologies. The catalytic performance of each catalyst was analyzed by studying the effects of their physicochemical properties through various characterizations, including XRD, SEM, BET, XPS, H₂-TPR, TEM and O₂-TPD. The characterization results demonstrated that the specific surface area, pore volume, high valence Co and Mn atoms, surface adsorbed oxygen and the abundance of oxygen lattice defects in the catalysts were the most critical factors affecting the performance of the catalysts. Based on the results of the performance tests, the catalysts prepared with an octahedral-shaped Fe-MOF loaded with Co and Mn showed a better performance than those loaded with Co and Mn on a rod-shaped Fe-MOF. The conversions of acetone and NO reached 50% and 64%, respectively, at 240 °C. The results showed that the catalysts were capable of removing acetone and NO at the same time. Compared with the pure Fe-MOF without Co and Mn, the loaded catalysts showed a significantly higher ability to remove acetone and NO simultaneously under the combination of various factors. The key reaction steps for the catalytic conversion of acetone and NO on the catalyst surface were investigated according to the Mars–van Krevelen (MvK) mechanism, and a possible mechanism was proposed. This study presents a new idea for the simultaneous removal of acetone and NO_x by photothermal coupling. Full article

In recent decades, numerous studies have indicated the substantial role semiconductors could play in photocatalytic processes for environmental applications. Materials that contain a semiconductor as a photocatalyst have a semi-permanent capacity for removing harmful gases from the ambient air. In this paper, the focus is on TiO₂. Heterogeneous photocatalysis using TiO₂ leads to the degradation of NO/NO₂, benzene, toluene, and other priority air pollutants once in contact with the semiconductor surface. Preliminary evidence indicates that TiO₂-containing construction materials and paints efficiently destroy the ozone precursors NO and NO₂ by up to 80% and 30%, respectively. Therefore, the development of innovative coatings containing TiO₂ as a photocatalyst was in the foreground of research activities. The aim of this was for coatings to be used as building and construction materials, mainly outdoors, e.g., on building façades on high-traffic roads for the degradation of priority air pollutants (NOx and volatile organic compounds) in the polluted urban atmosphere. Though there are advantages connected with the application of TiO_2, due to its band gap of 3.2 eV, these are limited. TiO₂ is effective only in the UV region (ca. 5%) of the solar spectrum with wavelengths λ < 380 nm. Hence, efforts are made here, as in many research studies, to dope TiO₂ with transition metals to increase its activity using visible light, which will extend its application to indoor environments. In our studies, experiments were conducted with 0.1% (w/w) and 1% (w/w) Mn-TiO₂ admixtures, and the ability of the modified photocatalysts to degrade NO by both solar and indoor illumination was evaluated. The surface chemistry at the air/catalyst interface, governed by the photoelectric characteristics of TiO₂ and the formation of reactive oxygen species with co-occurring redox reactions, is reviewed in this paper. The factors affecting the application of TiO₂ for the degradation of priority air pollutants as single compounds or mixtures are discussed. We investigated, particularly, the degradation of mixtures of priority compounds at typical concentrations in ambient air and confined spaces. This is a realistic approach, because pollutants are present as mixtures, rather than as individual compounds in ambient and indoor air. Moreover, organic polymers as paint constituents were found to be the primary source for carbonyl formation, e.g., formaldehyde, acetaldehyde, etc., during the heterogeneous photocatalytic processes conducted on TiO₂-enriched coatings. Full article

In the last few years, increasing interest from researchers and companies has been shown in the development of photocatalytic coatings for air purification and self-cleaning applications. In order to maintain the photocatalyst’s concentration as low as possible, highly active materials and/or combinations of them are required. In this work, novel photocatalytic formulations containing g-C₃N₄/TiO₂ composites were prepared and deposited in the form of coatings on a-block substrates. The obtained photocatalytic surfaces were tested for NOx and acetaldehyde removal from model air. It was found that the addition of only 0.5 wt% g-C₃N₄ towards TiO₂ content results in over 50% increase in the photocatalytic activity under visible light irradiation in comparison to pure TiO₂ coating, while the activity under UV light was not affected. The result was related to the creation of a g-C₃N₄/TiO₂ heterojunction that improves the light absorption and the separation of photogenerated electron-hole pairs, as well as to the inhibition of TiO₂ particles’ agglomeration due to the presence of g-C₃N₄ sheets. Full article

TiO₂ was loaded on the porous nickel foam from the suspended ethanol solution and used for the photocatalytic removal of NO_x. Such prepared material was heat-treated at various temperatures (400–600 °C) to increase the adhesion of TiO₂ with the support. Obtained TiO₂/nickel foam samples were characterized by XRD, UV–Vis/DR, FTIR, XPS, AFM, SEM, and nitrogen adsorption at 77 K. Photocatalytic tests of NO abatement were performed in the rectangular shape quartz reactor, irradiated from the top by UV LED light with an intensity of 10 W/m². For these studies, a laminar flow of NO in the air (1 ppm) was applied under a relative humidity of 50% and a temperature of 28 °C. Concentrations of both NO and NO₂ were monitored by a chemiluminescence NO analyzer. The adsorption of nitrogen species on the TiO₂ surface was determined by FTIR spectroscopy. Performed studies revealed that increased temperature of heat treatment improves adhesion of TiO₂ to the nickel foam substrate, decreases surface porosity, and causes removal of hydroxyl and alcohol groups from the titania surface. The less hydroxylated surface of TiO₂ is more vulnerable to the adsorption of NO₂ species, whereas the presence of OH groups on TiO₂ enhances the adsorption of nitrate ions. Adsorbed nitrate species upon UV irradiation and moisture undergo photolysis to NO₂. As a consequence, NO₂ is released into the atmosphere, and the efficiency of NO_x removal is decreasing. Photocatalytic conversion of NO to NO₂ was higher for the sample heated at 400 °C than for that at 600 °C, although coverage of nickel foam by TiO₂ was lower for the former one. It is stated that the presence of titania defects (Ti³⁺) at low temperatures of its heating enhances the adsorption of hydroxyl groups and the formation of hydroxyl radicals, which take part in NO oxidation. Contrary to that, the presence of titania defects in TiO₂ through the formation of ilmenite structure (NiTiO₃) in TiO₂/nickel foam heated at 600 °C inhibits its photocatalytic activity. No less, the sample obtained at 600 °C indicated the highest abatement of NO_x due to the high and stable adsorption of NO₂ species on its surface. Full article

Nitrogen oxide (NO_x) pollutants have a significant impact on both the environment and human health. Photocatalytic NO_x removal offers a sustainable and eco-friendly approach to combatting these pollutants by harnessing renewable solar energy. Photocatalysis demonstrates remarkable efficiency in removing NO_x at sub-scale levels of parts per billion (ppb). The effectiveness of these catalysts depends on various factors, including solar light utilization efficiency, charge separation performance, reactive species adsorption, and catalytic reaction pathway selectivity. Moreover, achieving high stability and efficient photocatalytic activity necessitates a multifaceted materials design strategy. This strategy encompasses techniques such as ion doping, defects engineering, morphology control, heterojunction construction, and metal decoration on metal- or metal oxide-based photocatalysts. To optimize photocatalytic processes, adjustments to band structures, optimization of surface physiochemical states, and implementation of built-in electric field approaches are imperative. By addressing these challenges, researchers aim to develop efficient and stable photocatalysts, thus contributing to the advancement of environmentally friendly NO_x removal technologies. This review highlights recent advancements in photocatalytic NO_x removal, with a focus on materials design strategies, intrinsic properties, fundamental developmental aspects, and performance validation. This review also presents research gaps, emphasizing the need to understand the comprehensive mechanistic photocatalytic process, favored conditions for generating desired reactive species, the role of water concentration, temperature effects, inhibiting strategies for photocatalyst-deactivating species, and the formation of toxic NO₂. Full article

This study explores the depollution activity of a photocatalytic cementitious composite comprising various compositions of n-TiO₂ and CaCO₃. The photocatalytic activity of the CaCO₃–TiO₂ composite material is assessed for the aqueous photodegradation efficiency of MB dye solution and NO_x under UV light exposure. The catalyst CaCO₃–TiO₂ exhibits the importance of an optimal balance between CaCO₃ and n-TiO₂ for the highest NO_x removal of 60% and MB dye removal of 74.6%. The observed trends in the photodegradation of NO_x removal efficiencies suggest a complex interplay between CaCO₃ and TiO₂ content in the CaCO₃–n-TiO₂ composite catalysts. This pollutant removal efficiency is attributed to the synergistic effect between CaCO₃ and n-TiO_2, where a higher percentage of n-TiO₂ appeared to enhance the photocatalytic activity. It is recommended that CaCO₃–TiO₂ photocatalysts are effectiveness in water and air purification, as well as for being cost-effective construction materials. Full article